Alternative Crash Severity Ranking Measures and the Implications on Crash Severity Ranking Procedures

Most states currently use ranking procedures to identify intersections with safety concerns. One objective of a state intersection ranking procedure is to provide a reliable start to the prioritization of safety improvements. For efficiency purposes, it is crucial to have a ranking system that identifies intersections with the most severe safety concerns. Otherwise, potentially hazardous intersections could be overlooked. Crash severity rankings are a part of many state safety management plans and are often used in combination with crash frequency and/or crash rate rankings. While the procedures for calculating crash frequency and crash rate at intersections are straightforward, there is no standard procedure for calculating crash severity. In fact, the methods used to define crash severity vary throughout the nation. Consequently, different approaches can produce different results, despite their common objective. The research presented in this paper had multiple objectives. The first objective was to introduce and describe a variety of used-in-practice crash severity ranking methodologies utilized by state DOTs. The second objective was to examine three years (1998 to 2000) of Wisconsin intersection crash data to identify or more closely define crash severity at intersections by exploring its relationship with crash type and vehicle damage. The third objective was to develop alternative crash severity ranking methodologies based on crash type and vehicle damage. The new crash severity ranking procedures developed from this work are then presented and compared to the results of four example state DOT ranking procedures.